Electro-optical display device

Claim 1

An electro-optical display device of the transmissive type which comprises: a linear polarizer for providing substantially linearly polarized light; a twisted nematic electro-optical cell positioned in the path of the light from said linear polarizer and capable of changing the state of polarization of said light, said twisted nematic electro-optical cell being composed of a pair of spaced transparent plates with a nematic liquid crystal filling the space therebetween and said plates having transparent electrodes provided on the opposed surfaces thereof; a 1/4-spectrum plate on the opposite side of said twisted nematic electro-optical cell from said linear polarizer for exhibiting one-quarter wave length retardation and producing circularly polarized light as its output; a cholesteric liquid crystal film on the opposite side of said 1/4-spectrum plate from said cell for selectively reflecting light of a specific wave length and exhibiting circular dichromism; means coupled to said cell for supplying an electric field to the nematic liquid crystal and including switch means for connecting and disconnecting said means from said nematic liquid crystal; a second 1/4-spectrum plate on the opposite side of said cholesteric liquid crystal film from said first mentioned 1/4-spectrum plate for receiving the light which is passed through said cholesteric liquid crystal film and for producing circularly polarized light as its output; a second twisted nematic electro-optical cell on the opposite side of said second 1/4-spectrum plate from said cholesteric liquid crystal film for changing the state of polarization of light from said second 1/4-spectrum plate; and a second linear polarizer on the other side of said second twisted nematic electro-optical cell from said second 1/4-spectrum plate for receiving the light from said second twisted nematic electro-optical cell and providing substantially linearly polarized light.